JP4853768B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a horizontal electric field type liquid crystal display device.

  A liquid crystal display device performs display by holding liquid crystal between opposing substrates and controlling the orientation of liquid crystal molecules with an electric field. In a twisted nematic (TN) liquid crystal display device, an alignment film on a counter substrate is rubbed in an orthogonal direction so that nematic liquid crystal molecules are twisted 90 degrees in a horizontal plane from one substrate to the other. When a voltage is applied between the electrodes on the counter substrate and an electric field is applied to the liquid crystal layer, nematic liquid crystal molecules rise up perpendicular to the substrate. A pair of polarizing plates is disposed outside the counter substrate. In the case of a cross polarizer having a transmission axis parallel to the alignment direction of the alignment film adjacent to the polarizing plate, incident light rotates with the twist of the nematic liquid crystal without applying a voltage, and passes through the cross polarizer (normally on). ). When voltage is applied and nematic liquid crystal molecules rise perpendicular to the substrate, the liquid crystal layer loses its optical rotation function. A cross-polarizer blocks incident light.

  If a pair of polarizing plates are arranged in parallel and parallel to either rubbing direction (for example, on the incident side), the incident light that has entered the liquid crystal layer without application of voltage and rotated 90 degrees is blocked by the output-side polarizing plate. (Normally off). In the voltage application state, the liquid crystal layer does not affect the polarization, so that incident light is transmitted.

  A normal liquid crystal material has a positive dielectric anisotropy in which the dielectric constant in the major axis direction of liquid crystal molecules is higher than the dielectric constant in the direction perpendicular to the major axis. In this case, in an electric field applied state, the liquid crystal molecules are aligned along the electric field direction. Liquid crystal molecules having negative dielectric anisotropy whose dielectric constant in the major axis direction of the liquid crystal molecules is lower than the dielectric constant in the direction perpendicular to the major axis are aligned in the direction perpendicular to the electric field direction when an electric field is applied.

  In order to apply an electric field in a direction perpendicular to the counter substrate sandwiching the liquid crystal layer, it is necessary to form electrodes on each of the counter substrates. However, the electric field direction for controlling the alignment of the liquid crystal molecules is not limited to the direction perpendicular to the substrate. The electric field in the substrate in-plane direction (lateral direction) can be generated by providing an electrode on the opposite substrate or providing an electrode on one substrate. Various liquid crystal display devices using a lateral electric field have been proposed.

In Patent Document 1, a counter electrode is formed on one substrate, a liquid crystal layer showing a twist is filled between the substrates, a voltage is applied between the counter electrodes, and an electric field in a horizontal plane is applied to control the twist. It proposes to transmittance plane switching for controlling (i n-plane switching) twisted nematic (t wistednematic) mode (iT mode) liquid crystal display device. An electrode pair arranged oppositely on one substrate is formed, and a voltage is applied between the electrode pair. A region between the electrodes becomes an electric field application region and becomes a display region. Although it is not necessary to use a transparent electrode, the electrode region is a non-display region. When the distance between the electrodes is increased, the generated electric field becomes weaker. When the distance between the electrodes is shortened, it is necessary to increase the number of electrodes per pixel.

JP 2002-268088 A

  An object of the present invention is to provide an IT mode liquid crystal display device having a novel configuration.

  Another object of the present invention is to provide an IT mode liquid crystal display device based on a new operating principle.

  Still another object of the present invention is to provide an IT mode liquid crystal display device having a high aperture ratio.

  Still another object of the present invention is to provide an IT mode liquid crystal display device that can easily generate a high electric field.

According to one aspect of the present invention,
First and second transparent substrates disposed opposite to each other;
A lower electrode formed on each pixel region of the first substrate;
An interelectrode insulating film formed on the lower electrode;
An upper electrode formed above a partial region of the lower electrode via the interelectrode insulating film;
Covering the upper electrode, a first horizontal alignment film formed on the interelectrode insulating film;
A second horizontal alignment film formed on the second substrate;
A nematic liquid crystal layer sandwiched between the first and second horizontal alignment films and exhibiting a twist in the thickness direction in the off state;
And at least one of the first and second substrates is a transparent substrate, and has no electrodes on the second substrate,
The lower electrode is a plurality of electrodes arranged along a first direction;
The upper electrode is a plurality of electrodes arranged along a second direction intersecting the first direction, each having a stripe-shaped opening;
There is provided a liquid crystal display device in which regions on both sides of the stripe-shaped opening of the upper electrode are electrodes arranged so as to sandwich the stripe-shaped opening above the surface of the lower electrode .

Since the upper electrode is formed so as to overlap the lower electrode, there is no space between the upper electrode and the lower electrode in the horizontal plane. Since both electrodes are disposed very close to each other, the electric field strength on the alignment film is also increased. Although the horizontal electric field is not uniform, a horizontal electric field is also formed above the electrode, and the display area can be expanded.

  The present inventors considered that in the IT mode liquid crystal display device, the first electrode and the second electrode are not arranged in parallel stripes on one substrate but arranged in an overlapping manner. That is, the lower electrode is formed widely, and the upper electrode is formed in stripes above the lower electrode via the interelectrode insulating film. There is a lower electrode without a horizontal gap below the periphery of the upper electrode. Although the horizontal electric field strength will change in the horizontal plane, the generation of a high horizontal electric field strength can be expected because the distance between the electrodes is short. Therefore, a simulation was performed to determine what electric field is generated in such an overlapping arrangement of the upper and lower electrodes.

  FIG. 1A is a cross-sectional view showing a model structure used in the simulation. A lower electrode 12 is formed on the entire surface of the first transparent substrate 11. An interelectrode insulating film 13 having a relative dielectric constant of 7 and a thickness of 6.67 μm is formed on the surface of the lower electrode 12, and a striped upper electrode 14 is formed thereon. The upper electrode 14 has a configuration in which a unit having a width of 20 μm and a space of 20 μm formed on both sides is used as a unit, and two units are arranged in one pixel. That is, the horizontal dimension of one pixel is 120 μm, and the lateral distance between the upper electrodes 14 is 40 μm. The distance between the upper electrodes 14 (horizontal direction) is 40 μm, whereas the distance between the upper electrode 14 and the lower electrode 12 (vertical direction) is 6.67 μm.

  The second substrate 21 is disposed at a position of 120 μm above the lower electrode 12, and the space between the substrates is filled with a nematic liquid crystal 19 having a relative dielectric constant of 10. The figure shows a state in which the pixels PX1 and PX2 are arranged side by side in the horizontal direction, but each pixel is equivalent and simulation was performed within one pixel region. The cross-sectional dimension for one pixel is 120 μm × 120 μm. For example, the lower electrode 12 is set to the ground potential, and the selected voltage is applied to the upper electrode 14.

  FIG. 1B schematically shows the shape of the lines of electric force when a positive voltage is applied to the upper electrode 14. Since the electric lines of force are perpendicular to the conductor surface on the conductor surface, the electric lines of force will be distributed vertically on the surface of the lower electrode 12. The lines of electric force generated from the lower surface of the upper electrode 14 will travel almost directly below the fringe portion and will enter the lower electrode 12 perpendicularly. The lines of electric force emanating from the side surfaces of the upper electrode 14 will initially be in the horizontal direction and will suddenly bend downward. The lines of electric force emitted from the upper surface of the upper electrode 14 are initially directed upward in the vertical direction, but spread as they move away from the upper electrode 14 (addition of a lateral component), change its direction, and eventually reach the upper surface of the lower electrode 12. The shape will be perpendicularly incident.

  The direction of the electric force lines emanating from a position close to the end of the upper electrode 14 will change direction more rapidly. The lines of electric force generated from the center of the upper surface of the upper electrode 14 are initially directed upward in the vertical direction, but eventually must enter the lower electrode 12, and gradually change its direction to some extent upward to generate a lateral electric field. Will do. Regarding the thickness direction of the liquid crystal layer, the lateral electric field strength will decrease as the distance from the lower substrate increases. Regarding the in-plane direction of the substrate, the lateral electric field strength is highest immediately outside the upper electrode 14, and becomes weaker as the distance from the end of the upper electrode 14 decreases.

  As a result of the simulation, it is confirmed that the lateral electric field is generated above the central portion of the upper electrode 14 and above the lower electrode central portion between the upper electrodes 14, but when the lateral electric field is slightly shifted, the lateral electric field is generated. It was. Therefore, a liquid crystal display device having such an electrode arrangement was designed. In the simulation model, the cell thickness was assumed to be 120 μm and a square pixel was assumed, but in an actual liquid crystal display cell, the cell thickness was about 4 μm. Even if the cell thickness (= liquid crystal layer thickness) is changed from 120 μm to 4 μm, only the dielectric such as glass and alignment film exists on the upper substrate. The shape of is not expected to change significantly. On the lower substrate, the alignment of the liquid crystal molecules was controlled by the electric field strength, and on the upper substrate, a measurement sample was prepared with the expectation that the anchoring force by rubbing was superior to the lateral electric field strength, and an operation test was performed.

  FIG. 2 schematically shows the configuration of a liquid crystal display device common to a plurality of embodiments of the present invention. An ITO transparent electrode 12 that is a lower electrode is formed on the surface of the glass substrate 11 that is the first transparent substrate. A silicon nitride film 13n having a thickness of 400 nm to 600 nm is deposited on the surface of the lower electrode 12 by plasma enhanced chemical vapor deposition (PE-CVD), and a silicon oxide film 13x having a thickness of about 300 nm is formed thereon by sputtering. accumulate. Thus, the interelectrode insulating film 13 is formed by insulating lamination. An ITO transparent electrode having a width of 20 nm is disposed on the interelectrode insulating film 13 as an upper electrode 14 with a space of 40 μm. The arrangement of the upper electrode is the same as that performed in the simulation. A horizontal alignment film 15 having a thickness of 50 nm to 100 nm is formed so as to cover the upper electrode 14. A horizontal alignment film 25 having a thickness of 50 nm to 100 nm is also formed on the surface of the second transparent substrate 21. As the horizontal alignment film in the measurement sample, a low pretilt alignment film SE-410 (manufactured by Nissan Chemical Industries) was used.

  In the first embodiment, the first alignment film 15 is rubbed in a direction parallel to the stripe-shaped upper electrode 14, and the second alignment film 25 is a direction orthogonal to the rubbing direction of the first alignment film. Rub to. The liquid crystal layer 19 is formed by adding a chiral agent that gives a twist of less than 90 degrees to a nematic liquid crystal having a positive dielectric anisotropy. The liquid crystal layer 19 in the measurement sample has a refractive index anisotropy of 0.1186 and a relative dielectric anisotropy of 11.5. Polarizing plates P1 and P2 having transmission axes in a direction parallel to the rubbing direction of adjacent alignment films are disposed outside both transparent substrates. Even if the transmission axis of the polarizing plate is orthogonal to the rubbing direction of the adjacent alignment film, the same characteristics can be obtained.

  FIG. 3A is a schematic diagram showing extracted characteristics of the liquid crystal cell according to the first embodiment. The lower polarizing plate P1 has a transmission axis in the longitudinal direction in the plane, and the rubbing direction of the alignment film 15 thereabove has a rubbing direction R1 parallel to the polarization axis P1. The upper polarizing plate P2 has an in-plane lateral polarization axis, and the rubbing direction R2 of the lower alignment film 25 is a lateral direction parallel to the polarization axis P2. The liquid crystal molecules in the liquid crystal layer 19 are aligned in the in-plane vertical direction in the region in contact with the alignment film 15 and in the in-plane horizontal direction in the region in contact with the alignment film 25. Except for the electrode arrangement, it is the same as the well-known normally white (NW) type twisted nematic liquid crystal display device having a twist angle of 90 degrees.

  The dielectric anisotropy of liquid crystal molecules is positive, and when an electric field is applied, the major axis direction of the liquid crystal molecules is aligned in a direction along the electric field. Accordingly, when a voltage is applied between the lower electrode 12 and the upper electrode 14 to generate a lateral electric field, first, the liquid crystal molecules on the outer periphery of the upper electrode 14 receive a strong lateral electric field and are aligned in the in-plane horizontal direction. Will do. Then, the incident light from above that is polarized in the horizontal direction by the polarizing plate P2 does not change the polarization direction while passing through the liquid crystal layer, and is polarized light having a transmission axis in the lower vertical direction while maintaining the polarization in the horizontal direction. Incident on the plate P1. Since the polarization directions are orthogonal, the polarizing plate P1 blocks incident light.

  Within the pixel, in the region where the horizontal electric field is strong, the orientation of the liquid crystal molecules is strongly controlled and the above-described change will occur, but in the region where the horizontal electric field is weak, whether or not the liquid crystal molecules are sufficiently controlled. Is unknown. Therefore, a sample was actually made and its operation was observed. When a voltage was applied between the upper and lower electrodes, a striped blackened region first appeared. When confirmed with a photograph, it can be considered as both outer regions of the upper electrode. As guessed above, it is considered that the liquid crystal molecules were rearranged in the region where the electric field strength was high. As time passes, the blackened area expands. The higher the applied voltage, the faster the change, and the rate of change seems to follow the applied voltage.

  FIG. 3B is a graph showing changes in transmitted light when voltage is applied to three types of samples in which the width of the inter-electrode slit is 20 μm, 30 μm, and 50 μm according to the first embodiment.

  The measurement results when the width of the slit between the electrodes is 20 μm are shown by ◯ plots. The transmitted light intensity is about 27% when no voltage is applied. As the applied voltage increases, the transmitted light intensity gradually decreases. When the applied voltage exceeds 25V, the transmitted light intensity becomes almost zero. A transmitted light intensity of 0 means that the entire pixel area is shielded from light, and that liquid crystal molecules are sufficiently rearranged even in a region where the electric field strength is weak.

  After applying the voltage to 30 V, the applied voltage is gradually lowered. When the voltage drops, there is a wide area where the transmitted light intensity is maintained at 0 even in the area where the transmitted light intensity is shown when the voltage is increased, and the transmitted light intensity starts to increase only when the applied voltage becomes 7 V or less. When the applied voltage was returned to 0, the transmitted light intensity was about 23%. This characteristic is a so-called hysteresis characteristic, and shows that once a liquid crystal molecule is aligned by applying a strong voltage, the same alignment is maintained even if the voltage is lowered.

  The measurement results when the width of the slit between electrodes is 30 μm are shown by Δ plots. The sample characteristics were similar to those of the electrode slit width of 20 μm. First, the transmitted light intensity in a state where no voltage is applied is about 29%, which is higher than that in the case of an interelectrode slit of 20 μm. As the voltage increases, the transmitted light intensity gradually decreases. The transmitted light intensity when the slit width is 20 μm and the transmitted light intensity when the slit width is 30 μm change substantially in parallel. When the applied voltage was 27V, the transmitted light intensity was almost zero. The applied voltage was increased to 30V and then gradually decreased. As in the case of the slit width of 20 μm, when the applied voltage decreases, the state of transmitted light intensity 0 continues for a long time, and the transmitted light intensity rises when the applied voltage is 7 V or less. The on / off operation was confirmed for the samples having the electrode slit width of 20 μm and 30 μm at the driving voltage of 30 V.

  The characteristics of the sample having a slit width of 50 μm are shown by rhombus ◇ plots. In this case, almost no hysteresis was observed. However, the transmitted light intensity does not decrease to 0 at an applied voltage up to 30 V, and black display is not realized.

  Black display was realized in samples having slit widths of 20 μm and 30 μm. This means that the orientation of liquid crystal molecules is controlled over the entire pixel surface of the liquid crystal cell. That is, it is possible to control the alignment of the liquid crystal molecules even in a region where the electric field strength is weak. However, it took time for the liquid crystal molecules to finish alignment. If the liquid crystal molecules are first aligned in a region where the electric field strength is strong, the alignment will gradually affect the region where the electric field strength is weak.

  4A to 4C are cross-sectional views schematically showing the operation of the liquid crystal cell inferred from the above measurement results. FIG. 4A shows a state before voltage application. The liquid crystal molecules are aligned along the rubbing direction along the direction of the electrode 14 (in the direction perpendicular to the paper surface) on the surface of the lower alignment film 15, and with the electrode 14 along the rubbing direction on the surface of the alignment film 25. They are arranged in the orthogonal horizontal direction.

  As shown in FIG. 4B, when a voltage is applied between the electrodes, the orientation of the liquid crystal molecules is first controlled in the high electric field strength region around the upper electrode 14. At this time, it is considered that the liquid crystal molecules are not rearranged yet in the region where the electric field strength is weak in the central portion of the upper electrode 14 and the central portion of the slit, and the original alignment is maintained. When the liquid crystal molecules in the high electric field strength region are rearranged, the surrounding liquid crystal molecules are affected by the orientation of the rearranged liquid crystal molecules and gradually change the orientation.

  As shown in FIG. 4C, after sufficient time has elapsed, the liquid crystal molecules are rearranged in the entire area of the liquid crystal cell, and the orientation of the liquid crystal molecules in the entire area of the pixel is controlled by the applied voltage.

  In the first embodiment, a liquid crystal having positive dielectric anisotropy is used. A liquid crystal having a negative dielectric anisotropy can also be used. Since the liquid crystal molecules having negative dielectric anisotropy are aligned in a direction orthogonal to the electric field, it is necessary to adjust the rubbing direction.

  5A to 5D show a configuration of an NW type twisted nematic liquid crystal display cell using a liquid crystal having a negative dielectric anisotropy according to the second embodiment. The structure of the liquid crystal cell is that shown in FIG. The material of the liquid crystal 19, the rubbing direction in the alignment films 15 and 25, and the polarization axes of the polarizing plates P1 and P2 are different from those in the first embodiment.

  FIG. 5A is a diagram in which features of the second embodiment are extracted. First, the rubbing direction of the alignment film 15 of the lower substrate becomes a direction orthogonal to the direction of the slit electrode 14, and the transmission axis P1 of the outer polarizing plate is also set parallel to the rubbing direction R1. In the upper substrate, the rubbing direction R2 of the alignment film 25 is set in a direction orthogonal to the rubbing direction R1 of the lower alignment film 15, and the polarization axis of the outer polarizing plate P2 is set parallel to the rubbing direction R2. The transmission axes P1 and P2 of the polarizing plate may both be orthogonal to the rubbing directions R1 and R2, but are set parallel in this embodiment. The cell is filled with nematic liquid crystal having negative dielectric anisotropy. In the measurement sample, the refractive index anisotropy of the liquid crystal molecules was 0.1032, and the relative dielectric anisotropy was −5.0.

  When no electric field is applied, the liquid crystal molecules are aligned along the rubbing direction. Since the relative dielectric anisotropy of the liquid crystal molecules is negative, the liquid crystal molecules are aligned in a direction perpendicular to the electric field when an electric field is applied.

  FIG. 5B schematically shows the alignment of liquid crystal molecules in the state where no electric field is applied. On the lower substrate, the liquid crystal molecules are arranged in a direction orthogonal to the slit electrode 14, and on the alignment film 25 of the upper substrate, the liquid crystal molecules are arranged in parallel with the slit electrode 14.

  FIG. 5C shows the alignment state of the liquid crystal molecules immediately after the voltage is applied. The alignment of the liquid crystal molecules is immediately controlled outside the peripheral edge of the upper electrode 14 having a high lateral electric field strength, and the liquid crystal molecules are rearranged in the direction parallel to the slit electrode 14. Since the lateral electric field is weak above the center of the electrode, the liquid crystal molecules still maintain the original alignment state.

  As shown in FIG. 5D, after a sufficient time has elapsed, all the liquid crystal molecules in the cell are aligned under the influence of the lateral electric field. Thus, when the liquid crystal molecules finish the alignment control, the transmitted light intensity will change sufficiently. That is, in the arrangement shown in FIG. 5D, black display is realized.

  In the first and second embodiments, the case where the pair of polarizing plates are arranged orthogonally has been described. This is a case where normally white display is performed, and the polarization axes of the pair of polarizing plates are parallel. When arranged along either rubbing direction, normally black (NB) display can be realized.

  In the above-described embodiment, the lower electrode is realized by the common electrode formed on the entire surface, and the upper electrode is realized by the stripe electrode. When forming an actual liquid crystal display device, various electrode forms can be employed.

  6A and 6B show electrode structures when performing simple matrix display.

  In FIG. 6A, the lower electrode LE is composed of a plurality of laterally long stripe electrodes arranged side by side in the vertical direction, and the upper electrode UE is a plurality of stripe electrodes in a direction orthogonal to the lower electrode LE. It consists of Further, the upper electrode UE includes two opening slits SA extending in the vertical direction in the drawing per electrode. That is, an electrode slit that is long in the vertical direction is formed between the lower electrode LE and the upper electrode UE. The number of slits is not limited to two. For example, three or more longitudinal slits may be formed in the striped electrode.

  FIG. 6B shows another form. The overall arrangement of the lower electrode LE and the upper electrode UE is the same as in the case of FIG. 6A. The opening slit SA formed in the upper electrode UE is configured by a slit extending in the width direction of the upper electrode UE. Therefore, an opening slit SA that is long in the horizontal direction in the figure is formed between the lower electrode LE and the upper electrode UE. Two lateral slits are arranged in a region where one lower electrode and one upper electrode intersect, and notches are formed on both the upper and lower sides. Since the lower electrode exists under the notch, an electric field distribution similar to the slit region is generated.

  6A and 6B, since the direction of the electrode slit changes by 90 degrees, it is necessary to set the rubbing direction of the alignment film accordingly.

  The interelectrode insulating film is not limited to an inorganic material. In the third embodiment, different materials are used for the interelectrode insulating film. The configuration of the liquid crystal display device is the same as that in FIG. 2A. The interelectrode insulating film 13n was formed to a thickness of 2.3 microns by spin coating (800 rpm · 30 sec) with an acrylic organic insulating film. An interelectrode insulating film 13x having a thickness of about 300 nm was deposited thereon by sputtering. The cell thickness is 2.5 μm for normally white (NW) cells and 16.5 μm for normally black (NB) cells. As the liquid crystal, a high refractive index anisotropy (Δn) type (Δn: 0.2008, manufactured by Merck & Co., Inc.) was used. The rest is the same as in the previous embodiment.

  FIG. 7A is a graph showing changes in transmitted light when voltage is applied to three types of samples having an electrode width of 20 μm and an inter-electrode slit width of 20, 30, and 50 μm.

  The measurement results when the width of the slit between electrodes is 20 μm are shown by the ● plots. The transmitted light intensity is about 18% when no voltage is applied. As the applied voltage increases, the transmitted light intensity gradually decreases. When the applied voltage is 40 V, the transmitted light intensity is almost zero. A transmitted light intensity of 0 means that the entire pixel area is shielded from light, and that liquid crystal molecules are sufficiently rearranged even in a region where the electric field strength is weak. In the cell of this example, hysteresis did not occur, and the amount of transmitted light could be defined by voltage.

  The characteristics of the sample with a 30-micron slit between electrodes (（plot) were similar to those of 20 μm. The transmitted light intensity is about 18% when no voltage is applied. As the applied voltage increases, the transmitted light intensity gradually decreases. Although the decrease in transmitted light intensity is almost saturated at an applied voltage of 40 V, the black level is superior to the sample with a slit width between electrodes of 20 μm.

  In the sample (x plot) in which the slit width between the electrodes was 50 μm, the transmitted light intensity did not become 0 even when 50 V was applied.

  As described above, it was found that the behavior of transmitted light intensity with respect to voltage differs depending on the interelectrode insulating material. It is necessary to select the optimal interelectrode insulating film according to the application.

  FIG. 7B shows the characteristics when the polarization axes of a pair of polarizing plates are parallel. The meaning of the plot should be the same as 7A. ◆ The plot shows a sample with an interelectrode slit width of 50 μm. A very strong black display can be realized in the vicinity of the applied voltage 0, and the transmitted light intensity increases as the applied voltage is increased. It can be seen that this arrangement is more advantageous in terms of contrast.

  The amorphous TN alignment cell that does not rub the alignment film according to the fourth embodiment will be described below.

  The electrode structure on the lower substrate is the same as in the third embodiment. The cell thickness was 2.5 μm, and only a normally white (NW) cell was prepared.

  A polyimide alignment film (SE-410) was formed on both substrates, and an empty cell was fabricated by stacking the substrates on each of the substrates without performing the alignment treatment. The cell thickness was 15 μm. A liquid crystal having a positive dielectric anisotropy Δε in which a chiral agent (S-811: manufactured by Merck) was added in a predetermined amount with respect to the cell thickness was injected into this cell. The amount of chiral agent added was controlled such that the pitch p of the chiral agent was d / p = 1/4 with respect to the cell thickness d. Even if the liquid crystal and the cell are heated in the isotropic state by heating the liquid crystal and the cell above the liquid crystal's nat-isotropic (NI) transition point, the liquid crystal is injected at room temperature (nematic state) and then at a relatively high temperature. The heat treatment may be performed at about 150 ° C. or higher. The orientation of the cell thus fabricated is an amorphous orientation as a whole (amorphous orientation), but many domains (multi-domains) are formed, and each domain has an orientation state twisted 90 degrees between both substrates. Indicated.

  FIG. 8 is a graph showing changes in transmitted light when voltage is applied to three types of samples in which the width of the slit between electrodes is 20 μm, 30 μm, and 50 μm.

  The measurement results when the width of the slit between electrodes is 20 μm are shown by the ● plots. The transmitted light intensity is about 17% when no voltage is applied. As the applied voltage increases, the transmitted light intensity gradually decreases. When the applied voltage is 40V, the transmitted light intensity is almost zero. A transmitted light intensity of 0 means that the entire pixel area is shielded from light, and that liquid crystal molecules are sufficiently rearranged even in a region where the electric field strength is weak. In the cell of this example, hysteresis did not occur, and the amount of transmitted light could be defined by voltage.

  The characteristics (■ plot) of the sample in which the width of the slit between electrodes was 30 μm were similar to those of the sample having a slit width of 20 μm. First, the transmitted light intensity when no voltage is applied is about 17%. As the applied voltage increases, the transmitted light intensity gradually decreases. Although the decrease in transmitted light intensity is almost saturated at an applied voltage of 40 V, the black level is superior to the sample with a slit width between electrodes of 20 μm.

  The characteristics of a sample having a slit width of 50 μm are indicated by x. The transmitted light intensity was about 10% even at an applied voltage of 50 V, and the transmitted light intensity did not change much.

  Hereinafter, viewing angle characteristics measured with samples actually created according to the third and fourth embodiments will be described. The cell conditions are the same.

  The same direction as the slit direction of the upper electrode was defined as the vertical viewing angle direction, and the direction orthogonal to the slit was defined as the left and right viewing angle direction.

  9A and 9B show the viewing angle characteristics of a rubbing NW cell with an interelectrode slit width of 20 microns. Select the voltage so that the transmittance is equally divided between the maximum transmittance of 100% and the minimum transmittance (0%), and change the viewing angle direction with the same voltage applied. Measured (equivalent to 6 gradation display). It can be said that the ideal viewing angle characteristic is that the transmittance does not change depending on the viewing angle.

  The characteristics (right and left viewing angles) in FIG. 9A are exactly the ideal characteristics, and it can be seen that the brightness and contrast (including gradation) hardly change depending on the viewing angles. This can be said to be extremely suitable for a display requiring a wide viewing angle, such as for a liquid crystal television or an in-vehicle monitor.

  It can be seen that the characteristic (vertical viewing angle) in FIG. 9B increases as the viewing angle increases. Although this characteristic is not preferable, it can be said that there are few situations in which many displays look into the monitor from the upper and lower oblique directions, and there are no practical problems.

  10A and 10B show the viewing angle characteristics of a rubbing NB cell with an electrical slit width of 20 microns. A voltage was selected so that the transmittance was equally divided between the maximum transmittance and the minimum transmittance (0%), and the transmittance was measured when the viewing angle direction was changed with the same voltage applied (6 Equivalent to gradation display).

  Although the black display does not change at all depending on the viewing angle, the characteristic (left / right viewing angle) in FIG. 10A shows that the white display has a slight transmittance but decreases as the viewing angle increases.

  The characteristic (vertical viewing angle) in FIG. 10B shows that the transmittance of white display is changed although the black display is not changed at all. Since the black display does not change from any direction, it can be seen that a display with high contrast can be realized from any direction.

  11A and 11B show viewing angle characteristics of an amorphous NW cell in which the slit width between electrodes is 20 μm and the alignment film is not rubbed. The tendency is almost the same as in FIGS. 9A and 9B, and it can be seen that excellent viewing angle characteristics are realized. In the case of amorphous alignment, since the alignment film is not rubbed, the manufacturing process is simplified, which is advantageous in manufacturing.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, although a transmissive liquid crystal display device has been described, a reflective liquid crystal display device can also be formed. In the case of a reflective liquid crystal display device, the substrate facing the incident side substrate may be opaque. In the case of a reflective liquid crystal display device in which the upper substrate is a transparent substrate, the lower electrode, the upper electrode, and the lower substrate can be opaque. The twist angle is not limited to about 90 degrees. The rubbing direction and the polarizing plate transmission axis are preferably adjusted to the twist angle. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

It is sectional drawing of the cell for demonstrating simulation, and the fragmentary sectional view which shows distribution of a line of electric force. It is sectional drawing which shows the structure of the liquid crystal display device common to a several Example. 2 is a diagram schematically showing a configuration of a liquid crystal display device according to a first embodiment, and a graph showing characteristics of applied voltage versus transmitted light intensity of a manufactured sample. It is a schematic sectional drawing explaining operation | movement of the liquid crystal display device by 1st Example inferred from a measurement result. It is the diagram and schematic sectional drawing for demonstrating the liquid crystal display cell by a 2nd Example. It is a top view which shows the example of an electrode shape. It is a graph which shows the characteristic of the applied voltage with respect to the transmitted light intensity of the sample of the liquid crystal display device by a 3rd Example. It is a graph which shows the characteristic of the applied voltage with respect to the transmitted light intensity of the sample of the liquid crystal display device by a 4th Example. It is a graph which shows the viewing angle characteristic of the sample of the normally white liquid crystal display device by a 3rd Example. It is a graph which shows the viewing angle characteristic of the sample of the normally black liquid crystal display device by a 3rd Example. It is a graph which shows the viewing angle characteristic of the sample of the normally white liquid crystal display device by a 4th Example.

Explanation of symbols

11 First transparent substrate 12 Lower electrode 13 Interelectrode insulating film 14 Upper electrode 15 First alignment film 19 (TN) liquid crystal layer 21 Second substrate 25 Second alignment film P Polarizing plate R Rubbing direction Δε Dielectric constant anisotropy

Claims (13)

First and second substrates disposed opposite to each other;
A lower electrode formed on each pixel region of the first substrate;
An interelectrode insulating film formed on the lower electrode;
An upper electrode formed above a partial region of the lower electrode via the interelectrode insulating film;
Covering the upper electrode, a first horizontal alignment film formed on the interelectrode insulating film;
A second horizontal alignment film formed on the second substrate;
A nematic liquid crystal layer sandwiched between the first and second horizontal alignment films and showing a twist in the thickness direction in the off state;
And at least one of the first and second substrates is a transparent substrate, and has no electrodes on the second substrate ,
The lower electrode is a plurality of electrodes arranged along a first direction;
The upper electrode is a plurality of electrodes arranged along a second direction intersecting the first direction, each having a stripe-shaped opening;
A liquid crystal display device , wherein regions on both sides of the stripe-shaped opening of the upper electrode are electrodes arranged so as to sandwich the stripe-shaped opening above the surface of the lower electrode . The upper electrode, the liquid crystal display device according to claim 1, wherein at least one of the lower electrode is a transparent electrode. The striped opening, a liquid crystal display device according to claim 1 or 2, wherein formed with a plurality per each pixel. The liquid crystal display device according to claim 1, wherein the stripe-like opening extends in a direction along an extending direction of the upper electrode. The liquid crystal display device according to claim 1, wherein the stripe-shaped opening extends in a direction orthogonal to the extending direction of the upper electrode. The liquid crystal layer has a positive dielectric anisotropy, the first horizontal alignment film crystal of any one of claims 1 to 5 rubbing direction is the direction parallel to the stripe-shaped apertures of the Display device. Wherein a liquid crystal layer is a negative dielectric anisotropy, the liquid crystal display of any one of claims 1 to 5 which is a direction the rubbing direction of the first horizontal alignment film is perpendicular to the stripe-shaped opening apparatus. The first and second substrates are both transparent substrates, the lower electrode and the upper electrode are both transparent electrodes, and the first and second polarizations disposed outside the first and second transparent substrates. the liquid crystal display device of any one of claims 1-7 having a plate. The first and second horizontal alignment films are rubbed in an orthogonal direction, and the transmission axes of the first and second polarizing films are parallel or orthogonal to the rubbing directions of the first and second horizontal alignment films, respectively. The liquid crystal display device according to claim 8 . The liquid crystal display device according to claim 1 , wherein the first and second horizontal alignment films are not rubbed and the transmission axes of the first and second polarizing plates are parallel or orthogonal. The inter-electrode insulating film, a silicon oxide film, a silicon nitride film, an organic insulating film, a liquid crystal display device of any one of claims 1-10 is either of these layers. The liquid crystal layer is a liquid crystal display device of any one of claims 1 to 11 containing a chiral agent. Twist the OFF state, the liquid crystal display device of any one of claims 1 to 12 is approximately 90 degrees total thickness.

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